Not many doctors would persist
with a treatment that has so far given cancer to nearly
20% of the patients who've received it, especially when
those patients are young children. But that's precisely
what a team of British doctors are doing. When the disease
being treated is as deadly as severe combined immunodeficiency
(SCID), they argued in the December 18 edition of The
Lancet, there's little choice but to proceed.
SCID or 'bubble-boy disease' is
mercifully rare, affecting only one in 200,000 newborn
boys. Because patients effectively have no functioning
immune system, they must be isolated from all sources
of infection, and their longterm prospects for survival
have, until recently, been bleak without a risky bone
marrow transplant procedure.
As a single-gene defect, however,
SCID is amenable to gene therapy. Eleven boys with SCID
were treated in Paris with gene therapy and were able
to lead normal lives as a result. But this freedom was
short lived for two of the children. Earlier this year,
it was announced that they'd been diagnosed with leukemia.
They're now in remission following chemotherapy.
PLAYING
THE ODDS
The appearance of leukemia posed a dilemma to doctors
at London's Institute of Child Health, led by Dr Hubert
Gaspar, who were treating four boys using the same approach.
They made the difficult decision to continue and have
documented their success so far.
The treatment has allowed all four
children to emerge from their 'bubbles' and two no longer
require any additional medication. None have developed
cancer — so far. No one is more relieved than
the Parisian researchers. Dr Marina Cavazzana-Calvo,
of Paris' Necker Hospital, said: "The safety issue is
always a concern, but we hope that it will be limited
to only the two boys who have developed acute lymphoblastic
leukemia so far. Unfortunately, we cannot know whether
any of the other boys will develop a similar side effect."
An investigation of the Paris results
showed that the implanted gene patch affected a nearby
gene, and that the implanted gene was itself overactive,
a common occurrence with viral delivery systems. The
Parisian researchers said they're closer to understanding
why the gene therapy caused leukemia, and are working
on safer gene delivery methods.
|
